Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session PR3: Coronal and HV Discharges |
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Chair: Brooke Stutzman, U.S. Coast Guard Academy Room: State D |
Thursday, November 6, 2014 1:30PM - 1:45PM |
PR3.00001: Temporal evolution of the electron density produced by nanosecond repetitively pulsed discharges in water vapor at atmospheric pressure Florent Sainct, Deanna Lacoste, Michael Kirkpatrick, Emmanuel Odic, Christophe Laux A study of plasma discharges produced by nanosecond repetitive pulses (NRP) in water vapor at 450~K and 1~atm is presented. The plasma was generated between two point electrodes with 20-ns duration, high-voltage (0-20~kV) pulses, at a repetition frequency of 10~kHz, in the spark regime (2~mJ/pulse). Atomic lines measured by optical emission spectroscopy were used to determine the electron number density in this non-equilibrium water-vapor plasma. The broadenings and shifts of the H$_\alpha$ and H$_\beta$ lines of the hydrogen Balmer series and of the atomic oxygen triplet at 777 nm were analyzed. For a maximum reduced electric field of about 200\,Td, a maximum electron density of 2~x~$10^{18}$~cm$^{-3}$ was measured, corresponding to an ionization level of about 10$\%$. This ionization level is two orders of magnitude higher than the one obtained for similar NRP discharges in air at atmospheric pressure. [Preview Abstract] |
Thursday, November 6, 2014 1:45PM - 2:00PM |
PR3.00002: Fast-imaging and spectroscopic analysis of atmospheric argon streamers for large gap arc breakdown Michael Pachuilo, Francis Stefani, Roger Bengtson, Laxminarayan Raja A non-equilibrium plasma source has been developed to assist in the low-voltage arc breakdown of large electrode gaps. The source consists of a dielectric embedded wire helically wound around a confining cylindrical quartz chamber. Annular electrodes cap the ends of the quartz chamber. An argon feed gas is used to provide a uniform environment and exhausts to ambient atmospheric conditions. A negative polarity 50 kV trigger pulse is applied to the embedded trigger wire to initiate the arc breakdown. Application of the trigger pulse produces a localized coronal discharges along the inner surface of the quartz tube. The corona provides seed electrons through which streamers propagate from one of the main discharge electrode along the quartz surface until it reaches the opposite electrode to bridge the gap. Once the gap is bridged a spark over occurs and robust arc discharge is formed in the chamber volume. Fast imaging of the streamer propagation establishes its velocity in the range of $\sim$ 100 km/s. Spectroscopy of the streamer discharge in atmospheric argon has been conducted and electron temperature and number density estimated from a collision radiative model. Argon spectrum is dominated by neutral argon lines in the 650-950 nm range, and singly ionized argon lines are observed in the ultra-violet to near UV (300-400 nm). [Preview Abstract] |
Thursday, November 6, 2014 2:00PM - 2:15PM |
PR3.00003: The role of oxygen and nitrogen metastable states in the electrical breakdown of air John Lowke For the initial formation of an electrical discharge in air, an electric field of approximately 25 kV/cm is required at a pressure of 1 bar, corresponding to a value of E/N of $\sim$100 Td; E is the electric field strength and N the gas number density. Below 100 Td, rates of electron attachment to form negative ions are greater than for ionization, so that a discharge of electrons is impossible. However, in less than a microsecond, metastable molecules of oxygen and nitrogen are produced, which markedly change the character of the discharge. The singlet delta metastable state of oxygen detaches electrons from negative ions of oxygen. By far the largest collisional process is the production of the metastable vibrational states of nitrogen. Populations of these states become so large that there is a significant increase in electron energy through collisions of these states with low-energy electrons. Solutions have been obtained of the Boltzmann transport equation for various values of E/N to obtain rates of production of the various metastables. It is found that the effect of the metastable states of nitrogen increases the electron energy at low values of E/N by orders of magnitude, ionization still being significant at E/N $=$ 20 Td. An analysis is made of continuity equations of electrons, ions and metastables and it is concluded that sustaining fields during the electrical breakdown process can be as low as 5 kV/cm at 1 bar, or an E/N of 20 Td, which is a reduction of a factor of five from the initial breakdown fields. [Preview Abstract] |
Thursday, November 6, 2014 2:15PM - 2:30PM |
PR3.00004: Back corona enhanced organic film deposition inside an Atmospheric Pressure Weakly Ionized Plasma reactor Rokibul Islam, Shuzheng Xie, Karl Englund, Patrick Pedrow A grounded screen with short needle-like protrusions has been designed to generate back corona in an Atmospheric Pressure Weakly Ionized Plasma (APWIP) reactor. The grounded screen with protrusions is placed downstream at a variable gap length from an array of needles that is energized with 60 Hz high voltage. The excitation voltage is in the range 0-10kV RMS and the feed gas mixture consists of argon and acetylene. A Lecroy 9350AL 500 MHz digital oscilloscope is used to monitor the reactor voltage and current using a resistive voltage divider and a current viewing resistor, respectively. The current signal contains many positive and negative current pulses associated with corona discharge. Analysis of the current signal shows asymmetry between positive and negative corona discharge currents. Photographs show substantial back corona generated near the tips of the protrusions situated at the grounded screen. The back corona activates via bond scission acetylene radicals that are transported downstream to form a plasma-polymerized film on a substrate positioned downstream from the grounded screen. The oscillograms will be used to generate corona mode maps that show the nature of the corona discharge as a function of gap spacing, applied voltage and many other reactor parameters. [Preview Abstract] |
Thursday, November 6, 2014 2:30PM - 2:45PM |
PR3.00005: Plasma decay in O$_{2}$-containing mixtures after high-voltage nanosecond discharge Nickolay Aleksandrov, Evgeny Anokhin, Svetlana Kindysheva, Andrey Starikovskiy Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically in O$_{2}$:Ar, O$_{2}$:CO$_{2}$ and some other mixtures for room gas temperature and pressures between 1 and 10 Torr. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1-3) $\times$ 10$^{12}$ cm$^{-3}$ and the effective electron-ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. The balance equations for these particles were solved simultaneously with the equation for electron effective temperature. It was shown that the loss of electrons in this case is determined by dissociative and three-body electron recombination with O$_{2}^{+}$ ions. The rate coefficient of three-body electron recombination was determined for these molecular ions. When changing gaseous mixture composition, the frequency of electron energy relaxation was varied by many orders of magnitude. This allowed extracting the values of three-body electron-ion recombination for both thermalized and heated electrons. [Preview Abstract] |
Thursday, November 6, 2014 2:45PM - 3:00PM |
PR3.00006: NO density and gas temperature measurements in atmospheric pressure nanosecond repetitively pulsed (NRP) discharges by Mid-IR QCLAS Marien Simeni Simeni, Gabi-Daniel Stancu, Christophe Laux Nitric oxide is a key species for many processes: in combustion, in human skin physiology... Recently, NO-ground state absolute density measurements produced by atmospheric pressure NRP discharges were carried out in air as a function of the discharge parameters, using Quantum Cascade Laser Absorption Spectroscopy. These measurements were space averaged and performed in the post-discharge region in a large gas volume. Here we present radial profiles of NO density and temperature measured directly in the discharge for different configurations. Small plasma volume and species densities, high temperature and EM noise environment make the absorption diagnostic challenging. For this purpose the QCLAS sensitivity was improved using a two-detector system. We conducted lateral absorbance measurements with a spatial resolution of 300$\mu $m for two absorption features at 1900.076 and 1900.517 cm$^{\mathrm{-1}}$. The radial temperature and NO density distributions were obtained from the Abel inverted lateral measurements. Time averaged NO densities of about 1.E16 cm$^{\mathrm{-3\thinspace }}$and gas temperature of about 1000K were obtained in the center of the discharge. [Preview Abstract] |
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